1. Field of the Invention
The present invention relates to a microchip useful as a μ-TAS (Micro Total Analysis System) that is suitably used for biochemical testing of DNA, protein, cells, immunity, or blood, chemical synthesis, and environmental analysis, and more particularly to a microchip having a fluid circuit therein.
2. Description of the Related Art
In recent years, in the field of medicine, health, food, drug creation and so on, there is an increasing importance of sensing, detecting, or quantitating a biological substance such as DNA (Deoxyribo Nucleic Acid), an enzyme, an antigen, an antibody, protein, virus, or cells as well as a chemical substance. Therefore, various biochips and microchemical chips (hereafter, these are generally referred to as microchips) are proposed that can conveniently measure these.
Such a microchip can perform a series of experiments and analysis operations that are carried out in experiment laboratories within a chip of several cm square and having a thickness of several mm, thereby producing a lot of advantages such as reduction of the needed amount of the samples and reagents to be minute, reduction of the costs, increase in the reaction speed, enablement of testing with a high throughput, and enablement of obtaining a test result directly at the site of collecting the sample, so that the microchip is used suitably for biochemical testing, for example.
Among the microchips, a microchip having a fluid circuit in the inside thereof performs reaction, mixing, or detection of a specific component with use of the portions arranged at appropriate positions and minute paths (for example, having a width of several hundred μm) that connect these portions in an appropriate manner, constituting the fluid circuit. A series of operations within such a fluid circuit can be carried out by application of a centrifugal force to the microchip. As the aforesaid portions, a liquid reagent holding portion that holds liquid reagent to be subjected to reaction (or mixing) with a sample to be an object of testing, analysis, or the like, a measuring portion to measure the sample or the liquid reagent, a reaction (mixing) portion for subjecting the sample and the liquid reagent to reaction (or mixing), and a detecting portion for analyzing and/or testing the reaction liquid (or mixed liquid) can be mentioned.
In the meantime, as a method for quantitatively detecting a trace amount of an object substance contained in a sample by an antigen-antibody reaction, the ELISA (Enzyme-Linked Immunosorbent Assay, also referred to as the sandwich method) is a suitable method that is often used, and has advantageous features such as being capable of detecting the object substance with a high sensitivity and being excellent in the quantitativeness. The ELISA method is a method such that, after a bound body of an object substance and an enzyme-labeled antibody is bonded to an antibody immobilized to a solid phase such as beads, a color generating reaction is let to occur by adding a color-generating substrate, and quantification is performed by measuring the optical absorbance of the produced color-generating substance. Here, in the ELISA method, after a bound body made of the immobilized antibody, the object substance, and the enzyme-labeled antibody is formed, a step of cleaning the solid phase such as beads will be essential in order to remove the free enzyme-labeled antibody. Since the quantitated value will be largely affected when the free enzyme-labeled antibody is present, the cleaning must be carried out carefully and thoroughly.
In the case of quantitating the object substance by the ELISA method using a microchip having a fluid circuit therein, as a means for carefully and thoroughly cleaning the aforesaid beads, repetition of operations of introducing a cleaning liquid to the site (beads trap) loaded with the beads in the microchip, letting the cleaning liquid pass therethrough, and discharging the cleaning liquid can be mentioned as an example. However, by this method, the cleaning liquid is discarded each time the cleaning liquid is let to pass within the beads trap, whereby the measuring apparatus will have a very large scale such as necessitating a cleaning liquid supplying apparatus and an exhaust liquid collecting apparatus on the outside of the microchip, thereby degrading the inherent convenience that the microchip originally has.
Japanese Patent Laying-Open No. 2005-134349 discloses using a microchip having a liquid reservoir on one surface of a substrate, immobilizing an analysis object substance within the liquid reservoir, adding a bound body of a labeling substance and a partner capable of being specifically bound to the analysis object substance to perform a bonding reaction, and thereafter cleaning the liquid reservoir by removing the unreacted labeled partner. However, in this microchip, the site for performing the reaction and the site to be cleaned are formed on the outside surface of the microchip, so that the fluid circuit inside the microchip is not cleaned. Further, the microchip disclosed in the document also necessitates external apparatuses such as a cleaning liquid supplying apparatus and an exhaust liquid collecting apparatus.
As described above, no microchip is currently known having a structure in which a fluid circuit in the inside of the microchip or a part thereof can be efficiently cleaned without being accompanied by disassembly of the microchip.